1. Field of the Invention
This invention relates to an infinitely variable traction roller transmission in which the opposed surfaces of an input toric disc and an output toric disc provided on input and output shafts, respectively, disposed on the same axis cooperate with each other to form a toroidal cavity and traction rollers are disposed in the toroidal cavity and are engaged with the input and output toric discs so that a great torque is transmitted by a traction force created in the portion of engagement, and more particularly to an infinitely variable transmission which can continuously and smoothly accomplish the transmission ratio control of acceleration and deceleration by a small operating force and which is simple in structure and excellent in durability and moreover inexpensive.
2. Description of the Prior Art
Infinitely variable traction roller transmissions of the general type described above are known and various ones have been proposed. For example, the transmissions disclosed in U.S. Pat. Nos. 3,142,189 and 3,810,398 are provided with a hydraulic cylinder and a servo valve. In these transmissions, a trunnion rotatably supporting the traction rollers is displaced in the direction of a pivot axis by the hydraulic cylinder and as a result, pivotal movement of the trunnion about the pivot shaft is induced to vary the radii of the engagement circles of the traction rollers with the input and output toric discs and effect self-transmission action and also move the servo valve backwardly by the variation in the angle of pivotal movement of the trunnion, thereby returning the displacement in the direction of the pivot axis to a neutral position. However, the hydraulic servo mechanism is very complicated in structure and adjustment and requires a hydraulic source and particularly, the use of a servo valve is liable to cause hunting and also, such transmissions have been expensive and it has been difficult to make them compact and light in weight.
The transmission disclosed in U.S. Pat. No. 2,086,491 does not use a hydraulic pressure, but it uses a worm and a worm gear, a screw and a screw gear, a rack and a pinion, etc. to directly pivotally move the trunnion to thereby effect speed change. This transmission is not of the type in which the trunnion as previously mentioned is displaced in the direction of the pivot axis and thereby effects self speed change action, but is of the type in which the trunnion is forced to effect speed change and therefore, this transmission has required a great force for the speed changing operation and sudden speed change has been difficult with such device.
Also, in the transmission disclosed in U.S. Pat. No. 2,907,220, a support member rotatably supporting the traction rollers is supported by a ball screw device for movement in the direction of the pivot axis, and a great thrust load exerted on the traction rollers is directly exerted as a radial load on the ball screw, and this has offered a problem in respect of the durability of the ball screw and also, it has been impossible to make the bearing rotatably supporting the traction rollers large in size and this has also led to a problem in respect of the durability of the bearing.